1. Field of the Invention
The present invention relates to an optical integrated device for use in an optical pickup device which optically reproduces information recorded on a storage medium such as CD (Compact Disc), LVD (Laser Video Disc), DVD and the like and/or optically records information onto the storage medium. The present invention also relates to a method of manufacturing the optical integrated device.
2. Description of Related Art
As an example of the above described optical pickup device, Japanese Laid-open patent application No. 4-89634 discloses an optical pickup device which has a semiconductor laser serving as a light emitting means and provided on a semiconductor substrate. A phase film layer, a polarization film layer, a grating, an optical waveguide and a first light receiving portion are formed on the semiconductor substrate in a laminated fashion, and a second light emitting portion is formed at an edge of the optical waveguide.
In this optical pickup, when the semiconductor laser irradiates a laser light on the phase film layer with a predetermined depression angle, the laser light is transmitted through the phase film layer, is reflected by the surface of the polarization film layer and is converged and projected onto the information surface of the optical disc. The laser light diffracted and reflected by the information surface of the optical disc is transmitted through the phase film layer and the polarization film layer to be incident upon the grating. A major part of the reflected laser light passes through the grating to be the transmissive light directed to the lower part of the substrate, and the remaining part of the reflected laser light becomes the guided light which is propagated through the optical waveguide. The transmissive light is received by the first light receiving portion which generates a tracking error signal and an RF signal. The guided light is received by the second light receiving portion formed at the edge of the optical waveguide, and the second light receiving portion generates a focus error signal.
According to the above optical pickup device, since those components are integrated by the semiconductor substrate manufacturing process, the device may be miniaturized and the using efficiency of the light quantity may be improved.
However, in the above-described optical pickup device, the second light receiving portion for generating the focus error signal has such a special positional relation with the first light receiving portion that the second light receiving portion is positioned normal to the first light receiving portion and the optical waveguide. Hence, there is a problem that a general light receiving device cannot be used.
As a result, manufacturing the optical pickup device requires producing a new light receiving portion. Also, since the manufacturing steps are relatively complicated due to the above special positional relation, the manufacturing cost of the optical pickup increases.
It is an object of the present invention to provide a optical integrated device for use in an optical pickup device, which enables integration by the semiconductor substrate manufacturing process, miniaturization of the whole device, improvement of efficient use of light quantity, effective use of the existing manufacturing system, easy manufacturing and manufacturing cost reduction.
According to one aspect of the present invention, there is provided an optical integrated device for use in an optical pickup device which irradiates a light onto an optical information storage medium and receives a reflected light reflected by the storage medium, the optical integrated device including: a light wave coupling element for generating at least a guided light from the reflected light; an optical waveguide unit for propagating the guided light, the optical waveguide unit including a multiple optical waveguides and at least a clad layer formed between the optical waveguides; and a light receiving element for receiving the light from the optical waveguide unit.
In accordance with the optical integrated device, the light wave coupling element generates at least a guided light from the reflected light, and the optical waveguide unit propagates the guided light. The optical waveguide unit includes a multiple optical waveguides and at least a clad layer formed between the optical waveguides. The light receiving element receives the light from the optical waveguide unit.
In a preferred embodiment, the optical waveguides in the optical waveguide unit may have identical refractive indexes, and the clad layers may have identical refractive indexes.
The optical waveguide unit may include three or more waveguides, and the optical waveguide of an uppermost layer and the optical waveguide of a lowermost layer may have thicknesses larger than thickness of the optical waveguide at intermediate layer between the uppermost layer and the lowermost layer.
The light wave coupling element, the optical waveguide unit and the light receiving element may be formed on a semiconductor substrate in a laminated fashion, and the light receiving element may receive a radiated light which is radiated by the optical waveguide to the semiconductor substrate due to phase matching.
The optical integrated device may further include a light shielding film formed on the optical waveguide of the uppermost layer at a position corresponding to a position of the light receiving element. The light receiving element may read out information recorded on the storage media and read out position information indicating a position of the light irradiated on the storage medium on a surface thereof.
The light receiving element may read out focal point position information indicating a position of the focal point of the light with respect to the storage medium.
According to another aspect of the present invention, there is provided a method of manufacturing an optical integrated device for use in an optical pickup device which irradiates a light onto an optical information storage medium and receives a reflected light reflected by the storage medium, the method including the steps of: heat-processing a semiconductor substrate to form heat-oxidized film on the semiconductor substrate, except for a partial non-processed area; laminating a protection layer on the semiconductor substrate having the heat-oxidized film, except for the non-processed area; forming, on the non-processed area, an optical waveguide laminated unit in which optical waveguides and clad layers are alternately laminated; and forming an optical waveguide of an uppermost layer at an area including the area where the heat-oxidized film and the protection layer are formed and the area where the optical waveguide laminated unit is formed.
The step of forming the optical waveguide laminated unit may form the optical waveguides and the clad layers in a multi-layer structure by alternately laminating the waveguides and the clad layers for multiple times. The heat-processing step and the protection layer laminating step may include etching the non-processed area after the heat-processing and the laminating.
The nature, utility, and further features of this invention will be more clearly apparent from the following detailed description with respect to preferred embodiment of the invention when read in conjunction with the accompanying drawings briefly described below.